Dust separator



Feb. 20, 1951 A. H. DAVIS ETAL 2,542,634

DUST SEPARATOR Filed Nov. 29, 1947 5 Sheets-Sheet l y IN V EN TORS 14 ECH/BALD H DA V/S CHARLES IV HAY FebVZO, 1951 A. H. DAVIS ETAL DUST SEPARATOR 5 Sheets-Sheet 2 Filed Nov. 29 1947 5 S Y a N m E m AA W WD H mm mi 0 III N T 5 l IDS \l A A z Mm m 0 A z y H m 2 n 5y 5 M 5 WWA/ H 6 w M M 2 m m 0 M H 7 a s I S 7 2 D A G 1 1, m y W EQQ A W A. H. DAVIS ETAL DUST SEPARATOR T. I L KK 7 4 7 6 MW 9 1k 2 1 7 V- |\RJ|) m m 5 o d e f. 4 Fw .5

Feb. 20, 1951 A. H. DAVIS ETAL DUST \SEPARATOR '5 Sheets-Sheet 5 Filed Nov 29, 1947 ui iqz INVENTORS ARCH/BALD H- DA v/s CHARlt-S N- HAY Patented Feb. 20, 1951 DUST SEPARATOR Archibald H. Davis and Charles N. Hay, Sandusky, Ohio, assignors to The Apex Electrical Mfg. 00., Cleveland, Ohio, a corporation of Ohio Application November 29, 1947, Serial No. 788,850

3 Claims.

This invention relates to vacuum cleaners and to the separation of solid matter from gas by the applicaion of centrifugal and other forces to the gas and solid matter.

The principal object of this invention is to eliminate the undesirable dust bag of conventional vacuum cleaners and collect the dust and dirt in a receptacle which may be easily and conveniently emptied and cleaned. Another object is to separate the dust and dirt from the air stream in a vacuum cleaner with such a high degree of efficiency as to eliminate the necessity of using supplemental filters, water traps, and the like. Other objects are to maintain a constant air flow at the nozzle of the cleaner during use, eliminating the decrease of air flow and reduced efiiciency in a conventional cleaner as the bag or filter becomes clogged with dirt; and to separate the dust and dirt from the air stream before the air enters the fan or blower, so as to protect the fan from the dust and dirt in the air stream and permit the use of a fan of maximum efficiency. I

Another object of this invention is to combine in a single machine the advantages of both the upright or floor type cleaner and the cylinder or tank type cleaner by-combining a high efficiency fan with a dirt and dust separator in advance of the fan, so as to obtain the efliciency of the upright type of cleaner in cleaning rugs and the high vacuum characteristic of the tank type of cleaner for opertaing attachment cleaning tools.

Another object of the invention is to improve the centrifugal separation of solids from gases by subjecting the dust laden air to forces which rarefy and accelerate the air in a zone in which separation takes place, so that centrifugal force is increased, the massof the air is decreased, the viscosity'of the air is reduced by the reduction in temperature due to expansion thereby permitting dust particles to move more freely through the air, and the relative humidity of the air is increased so that the dust particles pick up more moisture and are increased in mass. In this way the separating efficiency is increased in an exponential ratio to the pressure drop through the separator, and by the use of a pressure drop of twenty to thirty inches of water complete separation for all practical purposes is obtained.

Further objects of the invention are to improve and increase the efiiciency of centrifugal sepaproduce in such a separator a plurality of interacting cyclones producing different amountsv of centrifugal force; to collect all of the material separated from the air stream in a single con- .tainer without interfering with the operation of I the cyclones and without permitting any of the separated material to become again entrained in the air stream; to maintain the separating efliciency of the centrifugal separator substantially, constant through a wide variation in the quantity of air passing through the separator in a given interval of time, so that the operation of the separator is not affected by variations in the extent to which the nozzle of the vacuum cleaner is sealed against the rug or other surface being cleaned; and to prevent large objects,

strings, lint and the like from being caught in' the inlet or the outlet of the separator or in the and other forces to the air and the entrained dust,

dirt and other foreign matter. Generally speaking, the dirt laden air stream entering the shell of the separator is subjected to axial and tangential forces of such magnitude as to cause the stream to move in a helical path along the shell and to force entrained solid matter radially toward the shell, the main body of the air stream v is then subjected to an axial force in the opposite direction and centripetal forces causing it to move in a smaller helical path in the opposite axial direction from the first helical path so as to develop an increased centrifugal force on the entrained particles, while the foreign matter "which has been forced against the wall of the shell continues to move in thefirst mentioned helical path into a dirt receptacle in which the air is whirling in the same direction as the air in the first helical path, but is sufficiently free of axial currents to prevent separated dust and dirt from being picked up and again suspended in the air. air moving in the inner helical path is considerably reduced in pressure, density, temperature and viscosity and entrained particles are sub-- jected to an increased centrifugal force and are thereby given sufiicient velocity and momentum in a radial direction to move through the entering air and intothe streamof foreign matter The forces are applied so that the 3 adjacent the shell which enters the dirt receptacle.

Referring to the drawings:

Fig. 1 is a perspective view illustrating the general arrangement of an upright vacuum cleaner according to the invention;

Fig. 2 is a sectional view of a centrifugal fan and motor assembly; 7 V 7 Fig. 3 is a longitudinal sectional view of the cleaner;

Fig. 4 is a bottom view of the same;

Fig. 5 is a view, partly in section, of the preferred form of dust separator and its mounting on the handle of the cleaner;

Figs. 6 and 7 are sectionalviews of' the same: taken on the planes indicated in Fig. 5;

Fig. 8 is a section taken on the plane indicated by the line 88 of Fig. 7;

Fig. 9 is an end view of a slightly modified form of separator;

Fig. 10 is a longitudinal section of the same'on the plane indicated in Fig. 9; v

Fig. 11 is a diagrammatic top plan view of an inlet embodying the present invention applied to a different form of separator; and

Fig. 12 is a perspective view of a section taken on the plane indicated by the line l2-l2 of Fig. 11.

The upright type of vacuum cleaner illustrated in Figs. 1 to '7 may embody a chassis which is a modification of those previously used in upright cleaners, the modification being to incorporate a dust separator and to accommodate the flow of air to and from the separator. In common upright cleaners air flows from the nozzle through the fan to a bag. In a cleaner according to this invention, the air flows from the nozzle through the dust separator, then through the fan, and is discharged into the air. Preferably, the dust collector is mounted on the handle of the cleaner to promote compactness of the body of the machine and to facilitate the disposal of dirt collected by'the separator.

In the illustrated embodiment the cleaner includes a frame casting supported by four wheels 2! and having an extension 22 at it'sforward end forming a nozzle. The casting 28 includes a downwardly extending'fiange portion 22a which surrounds the'cleaner and the wheels 2| and merges into the nozzle portion 22. "The casting 2!) includes a substantially horizontal wall portion 24 formed with an opening" 25 adapted to receive the motor and-fan as'sembly. Downwardly extending wall portions 26 of the casting form the rear walls of the nozzle portion 22 and merge into generally longitudinally extending ribs 21. The ribs 21 extend under the opening 25 and are supported laterally by ribs 28 extending in from the opposite sides of the flange 22a and by an integral web 29 bridging the ribs 2'! at one point.

A cover plate 30 is removably secured to the bottom of the nozzle portion 22 and extends rearwardly, spanning the space between the ribs 21 in advance of and contacting the web 29. Openings 3| in the cover plate 30 constitute the nozzle openings through which the brush 23 extends and through which the dust laden air is taken into the cleaner. A cover plate -32 is removably secured to the ribs 21 spanning the space between these ribs rearwardly of and contacting the web 29. This cover plate is also removable to permit the attachment of a suction hose for the usual cleaner attachments.

A motor and fan assembly 33 is secured to the casting 20 with its lower portion extending through the opening 25 in the horizontal plate 24, the junction being sealed by any suitable gasket. The motor and fan assembly includes a fan casing formed by a bottom plate 34 and a channelled rim 35, and a motor housing formed by a support 36 and a cover 37. The centrifugal impeller 38 of the fan is mounted on a shaft 39 rotatable in an antifriction bearing 49 supported in the center of the bottom plate 34. The motor 4! is supported in any convenient manner from the support 36.

A cover plate 43 and a handle pivot casting 44 enclose the motor and fan assembly 33 above the horizontal wall 24, forming a space which is sealed from the nozzle and which is open to atmosphere through holes 45 opening downwardly through the plate 24.

Cleaner attachments which operate by pressure rather than vacuum, such as spray guns and the like may be connected to the openings 45 by a saddle bridging these openings, or in any other convenient way.

An air inlet pipe 46 is secured to and opens into the cover 37, and the periphery of the channelled rim 35 is provided with one or more outlet openings 47 opening into the space Within the cover plate 43 and the casting 44. A pulley 48 threaded onto the lower end of the shaft 39 drives the brush 23 through the belt 49.

The dust separator 58 (Figs. 1 and 5) is preferably mounted on the handle 5|, which is of tubular construction and is divided, except at its upper end, into two branches 52 and 53 which serve as inlet and outlet conduits, respectively,

for theseparator. The lower ends of these conduits are mounted in right-angle swivel fittings 54 rotatably received in bushings 55 and 5t fitted in the pivot casting 44. The bushing 56 communicates with the fan inlet pipe 46, and the bushing 55 communicates with a conduit 51 through which the dust laden air flows from the nozzle. The interior of the nozzle 22 is connected to the conduit 5! through a passage 58 between the ribs 27, which is closed on the bottom by the cover plates 30 and 32 and the web 29, and on the top by "the horizontal plate 24 and the fan cover plate 34.

The dust separator 58 includes a substantially cylindrical shell portion 60 to which is secured a cap 6 l. A dust collecting receptacle 52 is removably connected to the lower open end of the shell member 60. At its upper end the shell member 66 has its interior wall converging inwardly in a substantially ellipsoidal shape as indicated at 63 terminating in a top wall 64. A tangential inlet opening is formed in a boss 65 immediately below the top wall 64. The boss 65 projects from the shell 6:) and is secured to the tubular member 52 in any suitable way, as by the'fiange 66 which may be welded to the member 52.

Generally speaking the inlet is a rectangular conduit decreasing in radius and increasing in axial depth proportionately, so as to maintain the desired cross-sectional area, which is wound around the shell about 270 and which is cut away where it is intersected by the upwardly converging walls of the ellipsoidal portion 63. In the preferred'arrangement the inlet opening 61, which extends axially through the boss 65, is substantially square'in cross section. At the point where the opening 67 breaks into the interior of the ellipsoidal portion 53 the lower flat wall 68 of the inlet opening is inclined axially downward at an-angle which, in the preferred form, is such as to increase the axial length of the inlet as the radius decreases, as will be explained. The junction between the downwardly inclined fiat bottom wall 68 of the inlet opening and the upwardly converging elliposidal side wall 63 of the shell 60 extends circumferentially a short distance about the shell 60 and terminates at the point 69, where the bottom wall of the inlet disappears. The flat top wall of the inlet opening 6'! lies in the plane of the top wall 64 of the shell 60. The substantially vertical outer side wall 10 of the inlet opening is formed with a constantly diminishing radius and gradually merges into the ellipsoidal wall 63, the junction being indicated by the line H in Fig. 5. The inner vertical side wall 12 of the inlet opening 61 terminates at the point where the inlet breaks into the interior of the shell 60, so that the inlet passage defined by the vertical side wall 10 of constantly diminishing radius and the downwardly inclined bottom wall 63 is open on its inner side to the interior of the shell 60. Thus the inlet opening increases in axial extent and decreases in radius and in radial depth as it progresses circumferentially around the interiorof the shell 60 and merges completely into the ellipsoidal shape of the portion 63 of the shell in less than 360, preferably at about 270. In this manner a rectangular stream of air entering the casing through the inlet opening 61 expand in an axial direction and decreases in radial depth so as to form a wide thin sheet of air as it engages the ellipsoidal contour of the portion 63, and at the same time the inlet is open on its inner side so that any foreign object small enough to pass through the inlet opening 61 can continue into the interior of the shell 66 without danger of being caught in a position to block or interfere with the inlet opening.

Figs. 11 and 12 show the preferred form of inlet according to the present invention applied to a cylindrical shell tobetter illustrate the operation and results. It will be understood that the novel inlet of this invention may be applied to a shell of any desired type or shape. As shown in Figs. 11 and 12, the inlet opening 61 is substantially square in cross-section and opens into a cylindrical wall 63. The inlet is Set so that the inner surface of the wall 63' is tangent to a plane parallel to the axis of the inlet and spaced outwardly from the plane defined by the inner edge of the inlet about one-fourth of the width of the inlet. Thus the inner edge of the air stream projected from the straight, square crosssectioned portion of the inlet is spaced inwardly from the wall 63' about one-fourth of the width of the inlet in the zone indicated by the broken line I20.

The outer vertical wall 10' of the inlet curves around the shell in a spiral path of diminishing radius and merges with the shell wall 63 at a point about 270 around the shell. The bottom wall 68 of the inlet slopes downwardly so as to expand the axial depth of the inlet in proportion to the decrease in the radial width between the outer wall 10' and the inner edge of the air stream indicated by the line I20 so as to main tain the cross-sectional area of the air stream substantially constant.

Thus the inlet is a nozzle substantially square in cross-section at the entrance end tapering to a wide thin stream having an axial width about twelve to sixteen times its radial thickness at the outlet end, which i wrapped around the shell for about 270. No inner wall of the inlet noz- 6 zle is needed since the air stream is held by cell trifugal force against the outer wall. In this way the air stream is delivered in a wide thin sheet against the inner wall of the shell, but without the use of a narrow nozzle opening-which would catch small objects entering the separator and become plugged or otherwise interfere with the operation. In a specific example, the inlet 6'! ismade of an inch square, and is set so that the inner edge of the air stream, in- (heated by the line I20, is spaced /1 of an inch in from the wall 63. Thus at the point where hand, if the air stream were directed into tli shell through a nozzle A of an inch wide and '3 inches high, any object which will not pass through a slot A of an inch wide would catch in the nozzle, collect dirt and lint, and ultimately plug the inlet.

The inlet illustrated in Figs. 5 to 8 operates in the same way and is incorporated into the separator in the same way,-although the walls are cut away in part by their intersection with the ellipsoidal wall 63. It i to be understood that the novel inlet may be used with any desired shape or type of shell into which it is desired to project the air in a wide thin stream.

The top wall 64 of the shell'fifi is formed with an outlet pipe 13 extending axially downwardly into the shell to a point beyond the point 69 at which the bottom wall 68 of the inlet merges into the ellipsoidal portion 63. Preferably the outlet pipe 13 extends substantially to the junction between the ellipsoidal portion 63 and the cylindrical portion of the shell 6!). A baffle plate M is supported within the shell 60 at or near the junction between the shell .60 and the dust receptacle 52. The baffle plate '54 is imperforate and has its periphery spaced from the interior of the shell 60 and the dust receptacle 62 by a narrow annular space 15,. Preferably the baffle plate 14 is secured to the lower end of a rod 16 which has its upper end secured in a boss I1 in the cap member GI and which extends axially through the outlet pipe 13 and the shell 60. This supporting arrangement for the baffle plate 14 permits the annular opening 15 to be uninterrupted circumferentially and also leaves the upper end of the dust receptacle 62 unimpeded.

It is to be understood that the baflie may be mounted in other ways and if, for example, it is mounted from the dust chamber 52 or someother part, it is unnecessary to extend the rod 16 through the outlet 13 and the interior of the separator.

The cap 6! may be formed with an ellipsoidal shape, as shown, in continuation of the external surface of the ellipsoidal portion 63 to improve the appearance of the dust separator. An outlet conduit 18 opening through a side wall of the cap 6| is secured to the tubular member 53, as by a flange is welded to the tube 53 around an opening 73a therein which registers with the outlet conduit 78. Immediately above opening 18a in conduit 53 a plug I 25 is installed to prevent flow of air above this point in conduit 53. A similar plug I26 is mounted in the tubular member 52 above the inlet opening 67!. The connections of the inlet conduit 65 to the tube 52 and 7. themutlet conduit i8pto the:tube;53;may constitute the solesupport for the shell Gdand. cap 6!, as-shown, or additional supportsmay. be provided ifidesired.

A cross member Silsecured to the two swivel fittings; 54-; extends across the. space-between the tubes; 52' and" 53,.below the bottom: of the ,dust, receptaclepfiE: and is formed with a, spring seat 8| carryinga spring 82 adaptedto engage in a,

soc k et:,8-3:*on the bottomof the dustreceptacle.

62 'I'herdustreceptacle, 62 at its; upper end'has.

a islidingjfitgwith the lower open endxofthe shell filLso thatit, may be pushed down;against, the.

p i ngrfil, and removed laterally from the: tubes 52. and: 5,3 foremptying. When in placethe dust. receptacle 162} is; held against; the; bottom of the,

shell 66: by the spring 82 and by thereduced: pressure; which exists in the; separator in:opera:-

:When: the: cleaner is; operated dirt laden, air enters the nozzle 22, passes through the passage 58 into the conduit 5;'i,,throughthe'bushing'iii,

the; inlet tube 52, and into, the separator 5%;

through the inlet opening 5?. Clean air leaves: the separator through the outlet pipe 13, the; interior of the cap 61-, the outlet conduit l8, the tube53, thebushing 56, and passes through the fan-inleticonduit 46 into the interior of the motor housing 31. The cleanair is permitted to'pass aroundthe motorto cool the same and enters the fanhousing through an axial opening" in the support 36. radially into the rim- 35,, from, which it enters the interior of the cover plate 43 through the hole or holes 41 and is'discharged to atmosphere through the opening 45.

In the separator itself, the dust laden air stream entering the shell St: through the inlet passage 57 iscaused to flatten radially andexpand axially by centrifugal force, which increases progressively as aresult of the diminish ing radius of the wall 19. As the air stream comes into'contact with the ellipsoidal wall in its first revolution about the shell, the ellipsoidal wall 63-converts a part of the centrifugal force developed by the-rapid whirling motion-of the airintoan axial force, driving the air into a downward helical path along the wall of the shell St. The curvature and extentoithe ellipsoidal' wall 63 are selected with respect to-the air velocity of a particular separator so as to impart suificient momentum to-the air stream to drive it downwardly alongthe-wall of the shell 69 past the lowerend of the-outletpipe' innd against the battle M.

The centrifugal-forcedeveloped' by the circumferentialcomponent of'the'movement of the-air stream urges the dust and dirt entrainedin the air radially outward toward the wall of the shell 66 as the air stream moves downwardly in the helical path. By reason of the fact that the dust laden air stream-is free-to-spread axially with consequent reduction oi its radial depth under the infiuence of the centrifugal force, the distance, through which each dust ordirt particle in the-incoming air stream must move in order to reach the wall of the shell E-S is reduced to a minimum. The rate at which any particular particle of dust or dirt moves radially outward through the air underthe influence of the centrifugal force depends upon its specific gravity" and upon the relation between the mass and shape of the particle, whichin turn-determines the resistance to the movement of that particurlakparticle through air of a given density and The fanblades 38 drivethe air viscosity; The heavier particles; andxthose. whose shape isisuch. as to minimize air resistance, are; quickly projected throughthe, air streamto the.

wall ofthe shell 56. Lighter particles and those having a. greater air resistance move. radially outward at a slower rate.

When the, downwardly moving helical stream:

of air admittedirom the inlet reaches the baffle "id substantially all of the air is drawn inwardly by the reduced pressure in the center of the, separator ina, generally spiral path above the. bafil'e. l Landthenis drawn upwardly in a helical path. substantially smaller in radius than the. first:

mentioned helicalpath toward the outlet pipe 13.-

"1 Thisreversalof the, axial direction of movement oftheair is effected by a combination of. factors.

In thefirst place; the force which produces. the; movement of the; air through the; separator re-- sults from'the fact that the pressure in the outlet; tube 73' is less: than the pressure in the inlet conduit 67, so that a flow of air is established:

from the inlet 81 to theoutlet pipe '13. Sincethe low pressure area produced in the separator below the inlet pipe i3 is confined by theimperiorate bafiie Hi, there is substantially no pressure;

difference acting to urge the air to pass through theannular opening '!5 into the dust chamber 62-, and at thesame time, a substantial pressure difference exists abovethebafileidurging theair radially inward along the upper surface of the:

bafiie It. The air in the downwardly moving helix along the wall of the shellfiil which is 10- catedradially inward from the edge of the an: nular opening 15 strikes, the baflie it so that. its momentum maintaining its movementin a downward direction is absorbed, and the only force resisting; movement of the air radially inward, toward the,reduced pressure-area inthe center of, the shell is the centrifugal force resulting from the whirling; of the air.

Particles of dirt and dust which are close to the; wallof the shell-(ill during the downward helical movement of the incoming air stream. are projected in a; continuation of their helicalpath downwardly along the wall of the dust chamber 52, and through the annular gap E5. The air, in:

the dust chamber rotates in the same direction astheincoming air in the outer helix so that the dust particles are transferred smoothly and;

without turbulence from the helically or spirallymoving air above the bafiie to the rotating body of, air below the bailie. The momentum inparted to the particles of dust and dirt moving in the helical path along thewall of the shell 60,- and the dust container, 52 causes those particles to move through the gap '55 and to be projected; to the bottomof the dust container 62. The dust particles are not carried back to the shell 88 be; cause there is insufficient axial movement of the air in the container 62 to entrain the dust.

The main body of the air stream, and any particles of dust and dirt which did not come close'to the wall of the shell 58 duringthe down.-

ward'helical movement of the air stream, move, inwardly above the baffle Hi and thenupwardlyin a helical path toward the outlet pipe, 73. In this movement the'air, stream has a circumferential, component of movement in the samedirection as the air at the outer. portionof the shell Eda-11d an axial-component of movement in the opposite direction, The linear rotational velocity;

of; the air'moving downwardly in the outer helix,

or, cyclone, is not reduced by drawing the air into the upwardly movinghelix or. cyclone, and since. the; radiusisreduced the. angular velocity-of the,

force them radially outward into the downwardly moving outer helix.

Since the entire body of air in the shell 60 above the baflie 14 is moving circumferentially in the same'direction, the static pressure of the air has a maximum value adjacent the wall of the shell 66 and decreases considerably to a minimum value at the center of the shell, Thus the density and viscosity of the air in the inner helix or cyclone is substantially less than the den ity and viscos ty of the air adjacent the wall of the shell 60, so that the air resistance to the movement of any particle of dust or dirt is less in the inner cyclone than in the outer cyclone. Thus particles whose shape is such that they move through the a r stream slowly in the outer cyclone under a given centrifugal force move more rapidly through the air in the inner cyclone under the same centrifugal force. This reduction in density and viscosity in the air in the inner cyclone, combined with the increased centrifugal force existing in the inner cyclone, increases by many times the speed at wh ch particles of dust and dirt are separated from the air and projected radially outward. In addition the long length of the inner c clone, caused by the fact that it starts at the baffle, gives the dirt time to pass outwardly into the outer helical air stream before the inner cyclone air enters outlet pipe 13.

Other factors also increase the effectiveness of the dust and dirt separation in the inner cyclone as compared to the outer cyclone. Since the pressure and density of the air entering the outlet pipe 53 is less than the pressure and density of the incoming air, and because air in a confined passageway expands in the direction of its movement, the linear velocity of the air in the inner cyclone T3 is greater than the linear velocity of the entering air since the mass of air leaving the separator is equal to the mass of air entering the separator. This increase in linear velocity further increases the centrifugal force.

Dust and dirt particles which remain entrained in the a r entering the inner cyclone above the baffle M are projected radially outward at a substantially increased velocity and with sufficient momentum to pass through the stream of incoming air forming the outer cyclone to a point near the wall of the shell 60, where they agglomerate with other dust and dirt particles and move downwardly in the outer helical path throu h the annular opening 15 into the dust chamber 62. In ths way particles having a spe ific gravity or air resistance such that they cannot be separated successfully from the air stream in the outer cyclone, are not only separated from the air in the inner cyclone, but are thrown outwardly with sufficient force to pass through the outer cyclone into the stream of dust and dirt moving along the wall of the shell 50 and are deposited in the dust chamber 62.

Thus in operation the entire body of air in the shell 60 is rotating rapidly in one direction, the outer portion of the air having a downward movement in a helical path and the inner portion having an upward helical movement. The air pressure in the shell is greatest around the wall of the shell and decreases to a minimum at the center, the variation in pressure having an exponential relation to the radius because of the increased centrifugal force of the upwardly moving inner portion of the body of air. The imperforate baflle 14 seals off the lower end of the inner cyclone and the low presure area. The incoming air is given suflicient momentum both circumferentially and downwardly by the tangential inlet and. the ellipsoidal wall portion 63 to drive the air stream in a helical path to the baffle 14, and to prevent any appreciable portion of the incoming air from short-circuiting to the low pressure area in the inner cyclone until it substantially reaches the battle 14. Thus the baffle may be located at any distance below the lower end of the outlet pipe 13 within which these conditions may be maintained with a given flow of air; Preferably the bafile is located as far from without impairing the air velocity by an excessive amount of friction against the walls of the separator so as to obtain the maximum possible length of the inner cyclone. However, the distance of the baflle 14 from the lower end of the outlet pipe -13 is limited by the available pressure for operating the separator since increasing this distance increases the pressure drop through the separator required to maintain the air velocity.

The size of the baflie 14 and the radial width of the gap 15 are determined first bythe requirement that the baflie shall extend across and seal ofi the extreme low pressure area created by the inner cyclone, and second by the requirement that the extent of axial flow of the air in the dust chamber 62 shall be so small as not to again entrain in the air" stream dust particles deposited in the dust chamber.

The annular gap [5 permits only a relatively small percentage of the total quantity of air moving downwardly in the outer helix to enter the dust chamber 62 with the stream of dust and dirt concentrated along the wall of the shell 60, so that substantially all of the air in the outer helix is separated from the dust and dirt and moves inwardly in a substantially spiral path above the baflle 14. This separation of the air from the dirt at the annular gap 15is efiected primarily by pressure, as distinguished from a mechanical skimming action. The body of air confined'in the dust chamber below the bafile 14 is entrained by, andcaused to rotate with the air in the outer cyclone in the shell 62. Thus for a short distance down from the baffle and for a radial distance from the separator wall equal to the annular gap between the baffle and the separator wall, the pressure decreases with the radius in the dust chamber 62 at substantially the same rate as the pressure varies with the radius in the outer cyclone in the shell 60, so that the pressure is the same above and below the annular opening 15 at any point in the radial depth of the annular opening. Thus so long as the outer edge of the baflle 14 is located radially outward beyond the. point at which the pressure in the shell is substantially affected by the inner cyclone, there is no substantial difference in the pressure above and below the gap l5. With no pressure difierence across the annular opening there is no appreciable air flow across this gap to carry entrained dirt from the dirt container back into the separator and the operation at the gap T5 is therefore primarily a smooth interchange of the dust and dirt particles from a stream of air in the shell 60 moving helically and spirally to a body of air in the dust chamber .62 rotating at the same speed as the air in the shell-0 withoutedd-ies orturbulence or substan- .tialgaxial movementof air through the-gap '15.

--There is-therefora-no close critical :limit to the radial extent of thegap J5, and itmay betmade -sufficientIy-Wide-to permit the ines passage of cigarette butts and similar debris that may :be .picked sup-by the nozzle into the .dust [chamvsher r ,2.

The interaction of @the inner and outer icy- ;clones within the separator itself; involves other -.-nov,e1=-eif-ects contributing to the high separat- -,i ng efficiency of the present invention. The drawing of I the 1 air -irom-, the outer cyclone into :the ,inner cyclone against. the action of centrifpgal :iorce reduces the pressure, increases the ;;l l ne ar velocity of the ,air in thewinner cyclone and reduces the ;radius -of :the whirling motion 41f :the air. Theicentrifugal force-is thereby increased, I producin a large reduction in pressure near the axis- ;ofthe .inner cyclone, and :a large pressure drop :across the separator. Contrary to the usual practice of attempting to keeothe pressure drop across the separator as low as possible in order-to'conservepower, in-thepre ent -;invention a high pressure -drop-is :us dto take :fdvantage ;of the accompanying phenomena.

Thus in accordance with this invention the :centrifugal force opposinathe wiihdrawal'ofithe air :from the separator is maintained at such ,magnitude as :to cause i a pressure {drop :exce ding 2,0 inches *ofzwater across theiseparator. Ihe reduction in pressure near I the ,axisuof the-inner ecyclonegreatly exceeds ithez-dropacross the separator for exam le, with: a pressure .dron I across the separator ,of 30 inches-of water :there'iis a negative pressure of about'fifl inches of water -;near the axis ;of the :inner cyclone. Under these conditions a number of cumulative .efiects .com- :bine to'give complete separation for all practical purposes. The reduced densitv-of the air .in'the {inner cyclone increases :the difference between "the s ecific gravities of the .a r and the dust particles. Thus a given centrifugal force imparts a greater outward acceleration to dust vparticles. pressure is accompanied by areduction in temperature, which reduces the viscosity, and an increase :in relative humidity of the air in the inner cyclone. Since :the dust particles are slightly hygroscopic, the *increase in relative humidity causesthem to pick up additional Water from the :air, thereby increasing their weight. While 'these various .efiects are insigniafi'cant-in the pressure ranges ordinarily used in air cleaning apparatus and processes, their eterzof-the shell 0011's made about lands? inches.

="I-hesinlet conduit Bl-is made M; of an inch square .and' has an air inlet velocity of about 9,000 feet per minute. In'this particular separatorthe baffle 141's located .6 inches be ow the top wall-St ci theshell stand the outlet pipe 13 projec s? At the same time the reduction :in

.inlet opening .6].

inches below ithe-,v.'all- -64 leaving-a space ofinches .from'the lowerend of the outlet pipeto the baiiie. The bafile I l-is made of suchdiameter that the; radial widthvof the gap I5is from about 4 to of aninch. The. outletpipe .13 in this particular embodimentuis cylindrical and hasan inside diameter of 1%:inches. ,The curvature in. cross'section of the ellipsoidal portion63 corresponds approximately toaicircular arc with a-radiusof 2%?01" an inch struck from a point on theioppositesideof theaxis about s of an .inchibelow the lower endrof the outlet pipe 13. It willbeunderstood that the invention is notlimited to these dimensi0ns,;or to'any of them, but that these.representrsuitable dimensions and pro- ;portionsfor a separator to beusedwiththe fan and=c1eaner having the foregoing characteristics.

The pressure drop I across the separator is also affected by the size-of the outlet pipe I3 relative .tothediameteroithe shell-Maud the size of'the Itisfound that as a general proposition the-operating .eificiency of the separator increases withvanincrease of the pressure drop-across the separator. However, with'a separator of the foregoing-dimensions and proportions producing a .pressuredrop of 30 inches of water with aniair fiow-of 46=cubic feet-per minute, the separator removes substantially in ex- .cessof..99.99% vby weight-of-householddust picked up=bythecleaner nozzle from-rugs. .In other words, if during-thelife-of a vacuum-cleaner embodying this invention it. removed 10,000 pounds of .dirt.f rom the user's home, less than one pound ,a flange 9.6-of .the shellsl by toggle-clamps -9'I fixed. to .the shell .and engaging lugs 98 on the cup.

The chambers and 194 are separated by a ibaffle disk 99-which is secured .by a .nut I00 to a supporting rod [0| fixed in the axis of the separator. .An annular passage I 02 betweenthemargin of the disk 99 and the cup provides for .fiow of .dust from the separating chamber into the. collecting chamber. The hafllemay be of conical form, as illustrated, or may befiat .as shown in Fig. ,5. The :upper end closure'of the chamber 90 and the air outletof the separator are provided by a fitting comprising the outlet i03-and an annular body I04 fitting in the'upper end of the shell 9| andsecured therein bywelding or in any other suitable manner.

The air outlet for the separating chamber con- ;of a pipe I05 mounted centrally in a disk separator, causing an iIlfiOWIOf air through the inlet HiL'which comprises. a straight entrance pipe. III of rectangular cross section tangent to the conical portion 92 of the shell adjacent the top thereof, and a spiral portion H2 of gradually diminishing radius. which extends approximately 270 around the separator casing. The upper wall of the inlet H8 is preferably in a plane perpendicular to the axis of the separator. The lower wall l I3 of the inlet, however, inclines downwardly from the end ofthe straight section HI of the inlet, the inclination being about one part in four. The bottom wall H3 of'the spiral inlet thus intersects the conical wall 92 of the separator shell along a conical helix indicated by the numeral 1 [4 in Fig. 10. When the outer vertical surface of the spiral inlet IE2 meets the cone 92, these surfaces intersect along an ascending conical spiral ind cated by the line I 15 of Fig.- 10. It will be noted that the outlet pipe I05 extends below the lowest point of the inlet spiral 89.

The increasing depth and diminishing radius of the spiral portion l i2 as it extends around the casing operates in the same way and achieves the same results as the inlet illustrated in Figs. 5-8. The air stream is caused to spread axially in a downward direction, and is delivered smoothly against the conical wall portion 92, which directs the air into a downward hel cal path as in the embodiment shown in Figs. 5-8. V

In this form of separator, as in the embodiment shown in Figs. 5-8, the air is forced to flow downwardly in an outer cyclone and upwardly in an inner cyclone, the dust and dirt passing smoothly and without turbulence into invention, are of such high efliciency for their size and for the operating pressure required that they may be used in vacuum cleaners and the like without supplemental filters. By the combination disclosed, it is possible to design the fan for maximum efiiciency, since the air is cleaned before it enters the fan and it is not necessary to space the fan blades from the casing and from each other sufiiciently to p rmit the passage of debris picked up by the noz le. It is also preferred to use with the separator a fan and motor assembly having a rising characteristic; that is, an assembly which produces a greater pressure drop as the inlet is restricted.

Thus for example, with the cleaner and s parator having the characteristics and dimensions given above, the fan and motor are arranged to produce a negative pressure of 42 inches of water with the nozzle engaging the rug in nor' mal position. The separator is constructed with a pressure drop of 30 inches of water and there is a pressure drop of 5 inches at the nozzle and 6 inches in the hose and connections. If the clean ng nozzle should be forced down firmly against the rug or other surface being cleaned,

the pressure drop across the nozzle is increased and air volume reduced. The reduced flow of air through the separator results in reduced pressure drop across the separator, but the rising pressure characteristic of the fan combined with reduced friction in the piping holds the separator above the 20 inch drop found to be a critical value. lihus the fan and motor are preferably constructed so that as the flow of air is reduced the fan is capable of producing a maximum negative pressure of about 60 inches T lof water, so that there is always sufiicientpres's. sure difference to maintain thepressure drop. above 20 inches across the separatorregardless of the extent to which the nozzle is pressed against the surface being cleaned. In thisway the separating efiiciency of the separator, which varies in general with the pressure drop across the separator, is maintained substantially con-J stant regardless of the variations in the flow of air.

While the present separator has efficiency such that supplemental filters are not required, it is to be understood that the invention is not limited to a construction in which there are 'nosupplemental filters. For example, to avoid the possibility that the minute quantities of dust passed by the separator during a long period of use may collect in the motor or fan casing and be shaken loose and discharged in a pufi, it is possible to incorporate supplemental filters on the outlet side of the separator which would prevent the discharge of fine dust accumulated over a long period, but which would not need to be changed during the normal use of the cleaner to maintain the operating eificiency. In the embodiment disclosed, this danger is avoided by the arrangement of the atmospheric openings 45, which are directed downwardly toward the surface being cleaned.

It will be understood that the novel separator disclosed and the novel method of separating solid matter from gas may be employed for many other purposes and that many variations and modifications, both in the separator and in the combination of the separator with a vacuum cleaner, may be resorted to without departing from the scope of the invention as defined in the following claims.

What is claimed is:

l. A device for cleaning air flowing therethrough comprising a casing in the form of a surface of revolution and defining a separating chamber therein, an air inlet tangential to said casin at the first end thereof, an air outlet tube extending into the first end of the chamber axially and having its mouth normal to the axis of the chamber, said tube having an axial extent exceeding the axial extent of the said air inlet, means defining an annular peripheral dust outlet at the second end of the chamber, and a closed dust receiver into which the dust outlet ouens, the portion of the casing adiacent the in et tapering toward the first end, and the air inlet including a s iral portion of decreasing radius and increasing depth merging into the ta ered portion of the casing.

2. A device for cleaning air flowing therethrough comprising a casin in the form of a surface of revolution and defining a separating chamber therein, an air inlet tangential to said casing at one end thereof, an outlet tube for cleaned air exten ing coaxially of the chamber in said one end thereof, the portion of the casing adjacent to the said inlet tapering toward said one end, said tapering portion of the casing having an axial extent exceeding the axial extent of said inlet, said air inlet including a spiral portion of decreasing radius and merging into the tapered portion of the casing, means defining an annular peripheral dust outlet at the other end of the chamber and a closed dust receiver into which the said dust outlet opens.

3. A device for cleaning air flowing therethrough comprising a casing in the form of a surface of revolution and defining a separating 155 chamben therein, an air. inlet. tangential to said casingiatone end'thereof, said inlet. merging with thezcasingin a spiral portion of decreasing.

radiusand increasing depth, said spiral portion beingraopen throughout its length toward the axisr'of the ohamber :to provide unrestricted passagerinto the chamber 'for" air-carried objects having'a cross section corresponding to the entrance -cross section of said inlet, an air outlet tube extending into said one end of the casing REFERENCES CITED The TolloWing'referenoes are of record in the file' of this-patent? UNITED STATES PATENTS Name Date Pratsch Sept. 22, 1891 Number Number: Name; Date 755,430 f- Allington: -.Mar.;22 1904: 878,126 Derby Feb. 4,- 1.908 964,717. Verrell July 19,1910

1,108,248 Schmitz Aug. 25,1914 1,342,152 Bennett; June 1,1920. 1,34%,146 Peck June 22, 1920 1,461,173 Bennett July 10, 1923 1,603,020 Boldt et al Oct. 12, 1926 1,607,744; Mabie Nov.'23, 1926 1,826,798 Lee Oct. 13,1931 1,929,025 Leathers" Oct. 3, 1933 2,010,129 Arnold .Aug. 6, 1935' 2,019,895 Dow ..NoV. .5, 1935 2,222,930 Arnold Nov. 26, 1940 2,295,101 Dunham Sept. 8, 1942 FOREIGN PATENTS Number Country Date 176,352 Switzerland July 1, 1935 OTHER REFERENCES l lowPatt'ern and Pressure Drop in Cyclone Dust Collectors, Shepherd and Lapple. Industrial and Engineering Chemistry, August 1939, pages 972-984. 

